It is known that a body of water can be purified by having air circulated through the water, that is, by aeration. Springston, U.S. Pat. No. 4,247,261 (incorporated herein by reference), discloses a structure which has been used to purify water in relatively small bodies of water, such as ponds and fish hatcheries. The Springston patent discloses a Venturi-type water pumping device which is immersible in a body of water. The device includes a sheath formed as a hollow, generally cylindrical housing having opposite outwardly flared ends. A propeller and electric drive motor mounted in the housing cause water to flow through the interior of the cylindrical housing. When used for water purification in such small bodies of water, structures of the type the Springston patent discloses are carried by moored floats such that the propeller axis and drive shift are generally vertically oriented and the upper edge of the cylindrical housing is a few inches below the water surface. Water from the body of water being purified is sucked by the propeller to flow through the lower end of the cylindrical housing as well as openings in a wall of the housing between the opposite outwardly flared ends. The water flows through the upper end of the cylindrical housing and to the surface of the body of water with sufficient velocity to be aerated as a result of bubbles being induced in the water. The foregoing structure has been found to provide satisfactory aeration for the relatively small bodies of water but it is not effectively used in larger bodies of water such as creeks, inlets, rivers, harbors, bays, etc., because the number of such moored floating structures required to purify the larger bodies of water would be very large, resulting in significant expenses due to capital and operating costs.